One thing I'd like to mention here is that when a show has been on the air as long as MitM, it's not uncommon for it to last a season or two beyond the first time the creator starts talking about it being the "last season." Look at "Friends" and how many claims of "this is the last season" they went through before they finally called it a day for real.
Of course, MitM could be a different story, but I guess my point is to hope for at least an eighth season for right now....if only because we've been told that the seventh could be the last! Besides, in my opinion the show is still marvelously entertaining, having weathered the character evolution, aging of kids, etc. quite well. With Malcolm approaching college age, there might be another season or two's worth of material to go, not to mention Dewey's rise to Messianic status in the Busey class, plus Francis and Piama's need to settle into a career-minded field and maybe have a child of their own. This show is too good to simply "go out on a high note" when there's so much potential for greatness still in it.